In a multilayer optical disk with a large number of stacked recording layers, the reflectance of each recording layer is generally designed such that the amounts of light reflected back from the respective recording layers are the same on a surface of incidence of a light beam. Meanwhile, the multilayer optical disk suffers from multiple reflection. With reference, for example, to a multilayer optical disk with eight stacked recording layers L0 to L7 shown in FIG. 1, for playback of the recording layer L0 as a target layer located farthest from a surface of incidence of a light beam of the optical disk, the light beam is focused on the recording layer L0, and is reflected off the recording layer L0. At the same time, the light beam is also reflected off the recording layers L1, L2, and L3 near the recording layer L0. The light reflected off the recording layers L1, L2, and L3 forms first, second, and third confocal spots on the back surfaces of the recording layers L2, L4, and L6, respectively. These spots generate interlayer crosstalk, which is hereinafter called multiple reflection CT.
There is a known conventional technique of reducing multiple reflection CT (see Patent Literatures 1 to 4), in which every distance between multiple recording layers of an optical disk is defined such that at least some of distances between the adjacent recording layers differ from each other.    [Patent Literature 1] Japanese Patent Kokai No. 2001-155380    [Patent Literature 2] Japanese Patent Kokai No. 2006-40456    [Patent Literature 3] Japanese Patent Kokai No. 2006-59433    [Patent Literature 4] Japanese Patent Kokai No. 2006-252752